1. Field of Invention
The present disclosure generally relates to solid state low bay LED lighting apparatus and systems with integrated thermal management.
2. Related Art
Practical applications for Light Emitting Diode (LED) technology have evolved rapidly in the recent past. An LED is a semiconductor based light source. LEDs have been used as indicator lamps in many devices, and are increasingly used for residential, commercial, industrial and street illumination applications. LED illumination devices are used in applications as diverse as consumer electronic products such as remote controllers, televisions, DVD players, and other domestic appliances. They are also used for aviation and automotive lighting (particularly brake lamps, turn signals and indicator) as well as in traffic signals, in low bay parking garages, and in neighborhood street lighting
An LED is often small in area and has limited light output range. A number of LED lighting designs have integrated optical components such lenses or reflective surfaces to shape dispersion and radiation patterns. The development of LED technology has caused their efficiency and light output to rise exponentially, with a doubling of light output occurring about every 36 months since the 1960s, in a way similar to Moore's law. The advances are generally attributed to the parallel development of other semiconductor technologies and advances in optics and material science. LEDs present many advantages over incandescent light sources including lower energy consumption, longer life, improved robustness, smaller size, faster switching, and greater durability and reliability. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management systems than compact florescent lamp sources of comparable output.
One limitation in the use of LED lighting is excessive heat generation and adequate thermal management. Photons that do not escape the semiconductor surface as light because of the angle of incidence are converted to heat, raising the temperature of the LED and any associated circuit board powering the LED. LED lighting performance largely depends on the ambient temperature of the operating environment. An increase of ten degrees can result in a twenty five percent reduction in luminous output. LEDs have also been developed to increase luminosity by increasing current flow. At higher currents, such designs further increase the heating of the LED, creating more concern regarding light output. Over-driving an LED in high ambient temperatures may result in overheating the LED package, eventually leading to device failure. Adequate heat management is needed to maintain luminosity and long life. This is especially important in illumination applications for automotive, aviation, municipal, commercial, and residential architectural applications where devices must operate over a wide range of temperatures and require low failure rates.
Traditionally, two general strategies have been used to manage heat, active and passive. Passive thermal management essentially has meant some type of heat sink design. There has been a variety of heat sink designs, but with current LED illumination applications, the appearance of the lighting fixture is very important to users and must match the aesthetic requirements of the surroundings. Most heat sink designs simply do not have the aesthetic appeal required for mass adoption in real world lighting applications, or do not adequately remove heat sufficient to maintain luminescent integrity and LED life.
U.S. Pat. No. 4,729,076 to Masami et al strives to lower the temperature of the LED array by attaching a finned heat sink assembly to an LED lighting array. However, there is an impediment or restrictor in the thermal transfer path from the light emitting diodes to the heat sink; namely, a resin filler or adhesive is used to attach the LED array to the heat sink, which is a very poor heat conductor. The Masami '076 patent recognizes the problem of positioning the heat sink within a traffic signal light housing, where it must exchange heat with the air within the housing. As noted in the Masami '076 patent, some means of ventilation must be provided by vents, louvers, fans or the like. These type of venting arrangement are not particularly effective in hot climates, and simply trap hot air within the enclosure with little heat exchange with the environment. Since the lens, reflector, and lamp assembly is not designed to enhance air flow excess heating in the signal housing may degrade the optical performance of the unit.
U.S. Pat. No. 6,045,240 to Hochstein, entitled “LED lamp assembly with means to conduct heat away from the LEDS” and it's related U.S. Pat. No. 5,785,418, entitled “Thermally protected LED array” disclose an electrically driven LED lamp assembly that draws excess heat from the LEDs mounted on a plate through the LED leads that are thermally connected to a second thermally conductive plate. A heat sink overlies the conductive plating and an adhesive layer of thermally conductive adhesive is disposed between the conductive plating and the heat sink to secure the conductive plating and the circuit board to the heat sink. This heat sink arrangement is complex from a manufacturing perspective and increases cost. The design is also limited in that if the ambient are is close to the same temperature as the heat sink no additional cooling can occur. This is problematic in hot climates.
United States Patent Application 20100315813 entitled “Solid state light unit and heat sink, and method for thermal management of a solid state light unit” describes a lamp assembly that manages thermal energy output from solid state lighting elements. The lamp assembly achieves enhanced cooling of light elements within the assembly by providing a heat sink having a plurality of thermo bosses protruding on a first side, and a plurality of heat sink fins on a second side. A printed circuit board is secured to the first side of the heat sink, and has a plurality of through holes that correspond to the size and locations of the thermo bosses, such that when the printed circuit board is secured to the heat sink, the thermo bosses extend into the through holes. Light elements are mounted to the printed circuit board such that the through holes are located beneath the surface area of the light element, allowing the thermo bosses to contact the back side of the light elements to provide an enhanced thermal conductive path between the light elements and the heat sink.
U.S. Pat. No. 6,481,874 to Petroski, entitled “Heat dissipation system for high power LED lighting system” also discloses a heat sink concept. Petroski uses a die that receives electrical power from a power source and supplies the power to the LED. A first side of a die support (die attachment) is secured to the die. A thermally conductive material, which acts as a heat sink, is secured to a second side of the die support. Heat within the die is transferred to the heat sink via the die support. An outer body housing is secured around the thermally conductive material. The heat is transferred from the thermally conductive material to an external environment via the outer body. In the preferred embodiment, the heat from the die is primarily transferred to the heat sink and then to the outer body via conduction, rather than radiation or convection.
U.S. Pat. No. 6,910,794 issued to Rice, discloses an automotive LED lighting system where the LED is thermally coupled to a heat transfer condensing tube or heat pipe. Heat is transferred to an evaporation area of the heat pipe. Fins are affixed to the heat pipe to assist in transfer of heat away from the heat pipe. In operation, the heat pipe is filled with a fluid such as water or some other acceptable refrigerant. As the LED operates, heat is generated and transferred to the evaporation area through the shell of the heat pipe and then to the fluid. As the temperature of the fluid reaches its boiling point, additional heat is drawn from the heat pipe and some of the fluid changes to a vapor state, expanding throughout the void of the heat pipe. As the vapor expands in the void, it contacts the heat pipe at a condensation area which is located remote from the area at or near which the LED is mounted. Since the shell of the heat pipe is cooler at the condensation area than the evaporation area, heat is transferred from the vapor to the heat pipe at the condensing area. Fins are placed external the heat pipe to assist in removing heat from the heat pipe, for example, by passing air over them. Accordingly, the condensing area is maintained at a temperature below the boiling point of the fluid. Thus, as the vapor contacts condensing area, heat is transferred from the vapor to the condensing area and out through the fins. This causes the vapor to condense into droplets of fluid which are directed to the area of the heat pipe near the LED. This design and related manufacturing process is complicated. Further, any diminished integrity of the heat tube will allow fluid to discharge from the tube and the system will fail.
U.S. Pat. No. 6,499,860, issued to Begemann, entitled “Solid state display light” discloses an LED lamp that is characterized in that the heat-dissipating means comprised of a metal tubal column that connects an LED embedded substrate and lamp cap. The outer surface of the column of the LED lamp is made of a metal or a metal alloy. This enables good heat conduction from the LED embedded substrate to the metal lamp cap. The LED lamp also includes a fan incorporated in the column, which generates an air flow during operation of the lamp to generate forced air cooling. This air flow leaves the column via holes provided in the column, and re-enters the column via additional holes provided in the gear column. By suitably shaping and positioning the holes, the air flow is led past a substantial number of the LEDs present on the substrate. One problem with this design is that the air circulates in an enclosed system and thus cannot dissipate hot air from the system. Although the fan produces increased air flow, it also undesirably and materially increases design, manufacturing and complexity of the lamp. It also generates audible sound from the fan, which is undesirable many applications.
U.S. Pat. App. No. 20040201990 entitled “transparent gas with high thermal conductivity” uses a design similar to traditional incandescent bulb design were an LED light source is mounted on a support structure. A light transparent globe encloses the light source and support structure, and an electrical input lead and return lead pass into the globe providing electrical energy to the light source. A low molecular weight gas fill, such as helium or hydrogen, is enclosed in the globe to be in thermal contact with the light source. The thermal conductivity of the fill gas cools the LED source and does not interfere with light transmission.
U.S. Pat. No. 4,595,338 entitled “Non-vibrational oscillating blade piezoelectric blower” discloses fan based on oscillations generated by a piezoelectric material. The fan includes a piezoelectric bender with a supports at its inertial nodes. Weights are attached to the bender to control the location of the inertial nodes. Flexible blades are attached to the bender at various locations and with their planes in various orientations. The blower also consists of two benders oscillating 180 degrees out of phase to further minimize vibration and noise. This fanning is useful for enhancing air circulation, but increases the number of moving parts which create maintenance issues. Failure to detect a failing fan can cause the LED to overhead and shorten its life.
U.S. Pat. No. 4,763,225 to Frenkel, et al., entitled “Heat dissipating housing for an electronic component” discloses a heat dissipating housing with a tub and an outer cover seated on the tub, which is hermetically sealed for an electronic circuit component. Heat generated at the LED and a semiconductor driver chip is transferred to finned heat sink attached to the exterior of the tub. This design depends on removal of heat to the surrounding environment and the aesthetics are not particularly desirable for most applications.
U.S. Pat. No. 7,556,406 granted to Petroski, et al., entitled “Led light with active cooling” discloses an LED lamp that includes a piezoelectric fan or synthetic jet to cool components of the lamp. Although this is an improvement over previous designs there are limitation in that air circulation within most LED fixture designs is contained in an enclosure, limiting air flow and requiring venting.
U.S. Pat. No. 7,344,279 to Mueller et al., entitled “Thermal management methods and apparatus for lighting devices” discloses various methods and systems for providing active and passive thermal or cooling for LED lighting systems, including radiating and convective thermal facilities, including fans, phase change materials, conductive polymers, potting compounds, fluid conduits, vents, ducts, pumps and other thermal facilities increasing air flow. The heat transfer means can be under control of a processor and a temperature sensor such as a thermostat to provide cooling when necessary and to remain off when not necessary. The thermal facility can also be a conduction facility, such as a conducting plate or pad of metal, alloy, or other heat-conducting material, a gap pad between a board bearing light sources and another facility, a thermal conduction path between heat-producing elements such as light sources and circuit elements, or a thermal potting facility, such as a polymer for coating heat-producing elements to receive and trap heat away from the light sources. The thermal facility may be a radiation facility for allowing heat to radiate away from a lighting unit. A fluid thermal facility can permit flow of a liquid or gas to carry heat away from a lighting unit. The fluid may be water, a chlorofluorocarbon, a coolant, or the like. A thermal conduction path conducts heat from a circuit board bearing light sources to a fixture housing, so that the housing radiates heat away from the lighting unit. Mueller's design is complex, requiring significant increases in cost as a result of increased component content and manufacturing complexity.
U.S. Pat. No. 7,819,556, issued to Heffington, et al., entitled “Thermal management system for LED array” discloses synthetic jet cooling technology that utilizes turbulent pulses of air generated from an electromagnetic actuator. The device has a chamber having a liquid disposed therein, an LED array having a first surface which is in contact with said liquid, and (c) an actuator adapted to dislodge vapor bubbles from said first surface through the emission of pressure vibrations. The devise uses a two-phase cooling system based on vibration-induced bubble ejection processes in which small vapor bubbles attached to a solid surface are dislodged and propelled into the cooler bulk liquid. Although effective, the costs for such a system in many applications if prohibitive and less costly solutions are desirable.
Active cooling systems such as described in the prior art are generally less desirable because of added production cost, manufacturing complexity, noise generated by the active cooling mechanism, and maintenance requirements.
Thus it is desirable to provide an LED lighting fixture that addresses the disadvantages of known LED illumination devices, particularly those associated with thermal management, light output and ease of installation. Accordingly, it is one object of the current invention to provide a low cost thermal dissipation system for an LED illumination fixture. Thus a need exists for a low cost LED lighting system with efficient thermal dissipation and light propagation properties. The present teachings provide such a system.